convert int to const int

I work on FMatrix to use the wonderful function 'svd' but it's a template whitch is : FMatrix < type, cinst int N, const int M> N and M are the dimensions of the matrix.

The problem is that i make a lot of calculs, I create a special vector and then I need to use my svd function on a FMatrix<float, vector.size(), vector.size()>
But size return a int and the template need a const int.
How to convert vector.size() to a const int N that i could use as my matrix dimensions as FMatrix <float, N, N>?

You cannot, simply. FMatrix needs a constant, known-at-compile-time, value. std::vector::size is not known at compile time, so it cannot be used with FMatrix.
If you have the source for the svd function, you can adapt it to be used with another matrix library.